Extreme precipitation events in the Sichuan Basin and their connection to mesoscale disturbances

Abstract: The Sichuan Basin (SB) is a region with frequent extreme precipitation during summer, principally as a result of its location and topography, with the most extreme events possibly leading to floodings and landslides. A better understanding of these extreme events’ characteristics and triggers could help to improve forecasting methods, while improving the knowledge about climate dynamics in the region is crucial for climate change studies. To study the characteristics of this extreme summer precipitation, the ten most extreme summer precipitation events of the years 2000-2018 were identified from station data and classified as local or organised events, and persistent or non-persistent events. In addition, satellite data was used to assess the spatial extent of the events and reanalysis data provided information about the regional and large-scale characteristics present during the extreme precipitation. The presence and influence of mesoscale disturbances during the events was also examined. The results indicate that local events are non-persistent (short-duration) events and organised events are persistent (long-duration) events. As most of the extreme precipitation events were organised and persistent, it was concluded that the most disastrous precipitation events in this region are connected with organised convection. Important differences in the regional and large-scale circulation were observed between the month of June and July, August months, and these differences represent the development of the summer monsoon. The significant distinctions between events and the climatology show the influence climate dynamics have on precipitation development in this region. In addition, Mesoscale Convective Systems (MCSs) and Tibetan Plateau Vortices (TPVs) present during the events had an influence on the precipitation development, notably for the formation of organised precipitation. We conclude that organised convection, changes in the large-scale circulation and formation of mesoscale disturbances shape the development of severe weather within the SB by combining the conditions for extreme precipitation to occur.